Currently, studies are conducted for the RACH transmission method in 3GPP RAN LTE (Long Term Evolution). The RACH is an uplink channel which a mobile station, which is a communication terminal, uses upon shifting from idle mode to calling steps. Information including communication terminal identification information (User Equipment-Identification: UE-ID), a pilot, an association request, a resource request and transmission power required to establish a scheduled channel is transmitted to the base station using this RACH.
The RACH is a contention-based channel and cannot be scheduled by the base station, and so a mobile station takes the initiative to select transmission resources (e.g. transmission timing, frequency and code) on a random basis. If transmission resource blocks such as frequency band overlap between a plurality of users and the RACHs collide, the base station cannot correctly receive or demodulate data, and the mobile station have to retransmit the RACH to the base station.
For example, when the slotted ALOHA in W-CDMA disclosed in non-patent document 1 is applied, and, as shown in FIG. 1, the base station selects one from predetermined resource blocks (slots A to E) on a random basis, and transmits the RACH.
Non-patent Document 1: “6. Random access procedure,” 3GPP, TS25.214 V6.6.0 (2005-06)